More favourite mad science tropes:
Flashy explosions as a result of errors in procedures that have no conceivable reason to involve any explosive substance
Lab coats in non-laboratory settings
All mad scientists being versed in mad psychology regardless of their ostensible mad field of study
“It comes to life and starts eating people” being a potential failure mode of literally every experiment
WIldly unethical ways of accomplishing goal that could have been achieved more easily without the crimes against humanity
[noun] reaction/inversion/overload, where [noun] is something that one would not customarily regard as being capable of reacting/inverting/overloading
The way that you can pinpoint the popular anxieties of the era of the story’s publication by looking at the form factor of the thing that turns people into face-eating monsters (e.g., weird potion versus nuclear radiation versus psychiatric fuckery, etc.)
QuAnTum
World-ending superweapons that are also people even though being a person has no bearing on the world-ending part
“What in God’s name?” “God had nothing to do with it!”